Wednesday, August 24, 2011

Service Bulletin 8-24: Rod End Bearing needs cap washers

We had a partial failure on a rod end bearing, on a lift strut.  The point of failure is where the lift struts attach to the fuselage.  The internal structure of the rod end bearing began to fail, and as a result, the rod end bearing might have slipped over the head of the bolt.   If this had happened, there is a strong possibility that the lift strut might have detached from the bearing bolt on the fuselage, with damaging or catastrophic results.  A simple solution is the addition of a cap washer.  We recommend immediately adding these washers to your aircraft before further flight.  It is important that the top washer is trimmed so that it does not hit or rub the lift strut. 

Failed Lift Strut Rod End Bearing

Another view of Failed Rod End Bearing
In order to prevent these rod end bearings from slipping over the head of the bolt, we are installing cap washers:

Cap Washers, with one trimmed
Here is a photo of the reassembled lift strut attach point, showing the rod end bearings and the cap washers.:

Cap Washers installed on lift strut

The bolt has been reinstalled, complete with quik release key (safety wire is of course also acceptable).

If you need these washers, please contact us and we will supply them at no charge.

The integrity of the rod end bearings should be inspected with each preflight.

1 comment:

OK Engineer said...

A picture is worth a thousand words. Referring to your first photo, note the creasing of the seal from the male shank and counter clockwise from there. This is caused by the head of the bolt rubbing against the seal as the wing is rotated from flying to folded position. I'm guessing that your strut angle is close to 30 degrees to horizontal. Most of these spherical rod bearings are designed for a 10 to 15 degree misalignment angle. If the bolt head rubbed the seal, then it is likely that the mounting angle exceeded the permissible misalignment angle. Granted that a washer will limit the misalignment angle, but the excess angle will then put stress on the bolt and the bolt head. Is the bolt holding this assembly to the fuselage angled from the vertical about 15 degrees or so? Or, is this a special rod bearing that can reach an angle of 30 degrees? If not, then these could be fixes.

The gouges on the inner member on both the top and bottom of the bearing look to be caused by jamming of the inner member to the outer member. If the misalignment angle was exceeded, then it is possible that the head of the bolt jammed the bearing and did not let the inner member rotate freely. The gouges represent positions where the inner member jumped from place to place as the wing was rotated. The entire lower surface is scarred and the seal damaged. This is further indication that the entire mechanism was jammed. Unless the mounting of this member is limited to within the specifications of the bearing, a washer will not fix the problem.

I would think that the distance from the end of the fuselage mounting bracket to the edge of the bolt should be at least one bolt diameter. If the bolt is angled, that would be the distance between the closest point to the edge. I note that this bracket is different than the one shown for your aluminum fuselage. That one looks to be a square aluminum tube.